The present invention relates to transponders, with emphasis on xe2x80x9cpassivexe2x80x9d transponders which derive their operating power from an external radio frequency (RF) source, and more particularly to transponders associated with a pneumatic tire for use in tire identification and transmission of pressure and/or temperature data.
Transponder or transceiver type identification systems are well known, and generally are capable of receiving an incoming interrogation signal and responding thereto by generating and transmitting an outgoing responsive signal. The outgoing responsive signal, in turn, is modulated or otherwise encoded so as to uniquely identify or label the particular object to which the transponder element is affixed. An example of such a transponder type identification system is disclosed in U.S. Pat. No. 4,857,893, issued Aug. 15, 1989 to Carroll and incorporated in its entirety herein. This patent describes a transponder device which receives a carrier signal from an interrogator unit. This carrier signal, of frequency F, is rectified by a rectifying circuit in order to generate operating power. Alternatively, the addition of a hybrid battery allows device to be converted into a self-powered beacon device. Logic/timing circuits derive a clock signal and second carrier signal of frequency F/n from the received carrier signal. A uniquely-identifying data word is stored in a Programmable Read-Only Memory (PROM). The data word is encoded and mixed with the carrier signal in a balanced modulator circuit, the output of which is transmitted to the interrogator unit where it is decoded and used as an identifying signal. All electrical circuits of the transponder device are realized on the same monolithic semiconductor chip which may be implemented as a Complementary Metal Oxide Semiconductor (CMOS) device.
In the manufacture of pneumatic tires, it is desirable to uniquely identify each tire as soon as possible during the course of its fabrication. This is generally done by assigning an identification (ID) number to each tire. The ability to uniquely identify tires throughout their manufacture is particularly valuable in quality control in order that the source of manufacturing problems can readily be ascertained. For example, statistical process control and other methods can be used with tire identification to detect process parameters that are going out of specification to detect machinery wear, failure, or maladjustment. The identification information should be easily discernible throughout the manufacturing process, including throughout post-manufacturing (e.g., inventory control) stages.
It is also beneficial to be able to uniquely identify a tire throughout its service life (use), for example for warranty determination, and retreading of the tire should not adversely affect the ability to identify the tire. It is also important that the tire identification be readily discernible when the tire is mounted on a steel or aluminum rim (as is normally the case), including when the rim is one of a pair of rims in a dual wheel assembly (as is common with tractor trailers).
Aside from being able to uniquely identify a tire at various stages in its manufacture and service life, it is beneficial to be able to monitor tire pressure when the tire is in use. As is known, proper tire inflation is important to proper tire performance, including road-handling, wear, and the like.
U.S. Pat. No. 4,578,992 issued Apr. 1, 1986 to Galasko, et al. and incorporated in its entirety herein, discloses a tire pressure indicating device including a coil and a pressure-sensitive capacitor forming a passive oscillatory circuit having a natural resonant frequency which varies with tire pressure due to changes caused to the capacitance value of the capacitor. The circuit is energized by pulses supplied by a coil positioned outside the tire and secured to the vehicle, and the natural frequency of the passive oscillatory circuit is detected. The natural frequency of the coil/capacitor circuit is indicative of the pressure on the pressure-sensitive capacitor.
U.S. Pat. No. 4,758,969 issued Jul. 19, 1988 to Andre, et al. and incorporated in its entirety herein, discloses a device for measuring brake temperature and tire pressure on sets of wheels. The temperature sensors are located on a fixed part of each wheel, and communicate with the central computer by means of wires. A pressure sensor is mounted on each wheel along with electronic means for frequency coding the pressure data. Between each wheel and the fixed part of each wheel is a coupling element, preferably a rotating transformer for communicating with the central tire pressure measuring system computer. The frequency coding electronics preferably include a voltage/frequency converter to convert a voltage constituting the signal delivered by the sensor into a frequency which is a function of said voltage.
The use of radio frequency (RF) transponders, located either within the tire or on a rim for the tire, in conjunction with electronic circuitry for transmitting a RF signal carrying tire inflation (pressure) data, is also well known.
An example of a RF transponder suitable to be installed in the carcass of a pneumatic vehicle tire is disclosed in PCT International Application Publication No. WO 96/064747 issued Mar. 7, 1996 to Andrew, et al. and incorporated in its entirety herein. This patent describes a tyre condition monitoring system with a battery-powered (xe2x80x9cactivexe2x80x9d) transmitter unit in each vehicle wheel for sensing temperature, pressure and rotation of the wheel. A common problem to be dealt with in such active systems is the life of the battery (power supply). The transmitter unit is arranged so that power is only applied during the sensing and transmission of data, and intervals between transmissions of data can be varied depending on whether rotation of the wheel has been sensed. The transmitter unit (RF transponder) includes a pressure sensor (either piezoresistive or silicon capacitive), a thermistor for temperature sensing and an input for measuring the battery voltage. These sensor measurements are periodically checked, being routed one at a time to an analog-to-digital converter (A/D) by a multiplexer. A microprocessor receives the digitized readings, preferably converts them to temperature and pressure units, and periodically transmits them. The microprocessor has RAM, ROM and inputs including the A/D, a clock, a timer, and centrifugal detector. It controls overall operation of the transmitter unit. An identification number (ID) is stored in non-volatile ROM memory, and calibration constants for data conversion are stored in battery-maintained RAM. In normal operating mode, the RF transmission, when required, includes the ID, the temperature reading, and the pressure reading. The number values in the transmission string are digitized and encoded for error correction using Manchester coding. The calibration constants are preferably used to convert the readings from voltages to suitable temperature and pressure units, but may alternatively be stored in the vehicle receiving unit and used therein to convert transmitted voltage readings. In order to minimize battery use by minimizing transmission times, the calibration constants are only transmitted on demand from the receiving unit, preferably upon tire installation. The calibration constants include one constant to convert temperature sensor voltage to degrees, and two constants to convert pressure sensor voltage to pressure units and also correct for the pressure sensor""s temperature coefficient.
An example of a RF transponder suitable to be installed in the carcass of a pneumatic vehicle tire is disclosed in U.S. Pat. No. 5,451,959 issued Sep. 19, 1995 to Schuermann and incorporated in its entirety herein. This patent describes a transponder system comprising an interrogation unit for communicating with a plurality of responder units. The responder unit contains a parallel resonant circuit having a coil and a capacitor for reception of a RF interrogation pulse. Connected to the parallel resonant circuit is a capacitor serving as an energy accumulator. A processor may be provided for receiving input signals from a sensor which responds to physical parameters in the environment of the responder unit 12, for example to the ambient temperature, the ambient pressure or the like. The sensor could for example be an air-pressure sensitive sensor. In this case the responder unit can be installed in the carcass of a vehicle pneumatic tire and, with the aid of an interrogation unit contained in the vehicle, it is possible to continuously monitor the air pressure in the tire.
Another example of a RF transponder suitable to be installed in the a pneumatic vehicle tire is disclosed in U.S. Pat. No. 5,581,023 issued Dec. 3, 1996 to Handfield, et al., and incorporated in its entirety herein. This patent describes a transponder and a receiving unit, preferably one transponder for each vehicle tire, and the transponder may be entirely disposed within the vehicle tire. The transponder includes a pressure sensor, and may include various other sensors such as a temperature sensor. An Application-Specific Integrated Circuit (ASIC) embodiment of the transponder is described. With reference to FIG. 9 of the patent, the ASIC (300) includes an oscillator (322) controlled by an external crystal (325), a constant current device (310) providing current flowing through an external variable-resistance pressure sensor (327), a window comparator circuit (324) having a lower threshold for reporting pressure information established by external resistors (329 and 331) connected in a voltage-divider arrangement, and an upper threshold controlled by an external variable resistor (333). A number of three-position jumpers (328) are utilized to program a unique transponder unit serial number during its manufacture. The ASIC (300) is powered by an external battery (318), and a transmitting circuit (312) is external to the ASIC (300).
Another example of a RF transponder suitable to be installed in a pneumatic vehicle tire is disclosed in U.S. Pat. No. 5,661,651 issued Aug. 26, 1997 to Geschke, et al. and incorporated in its entirety herein. This patent describes a wireless system for monitoring vehicle parameters, such as tire pressure. RF signals transmitted from different tires may be distinguished based upon the frequency of the transmitted signal. In order to sense the pressure inside a tire, tire pressure monitoring systems utilize a pressure sensor located within the tire. FIG. 2 of this patent shows the preferred structure for a parameter sensor and transmitter circuit when used to monitor the pressure inside a vehicle""s tire. Parameter sensor and transmitter circuit (20) includes a pressure-to-voltage transducer (21) and a battery-powered power supply circuit (24).
The need to monitor tire pressure when the tire is in use is highlighted in the context of xe2x80x9crun-flatxe2x80x9d (run deflated) tires, tires which are capable of being used in a completely deflated condition. Such run-flat tires may incorporate reinforced sidewalls, mechanisms for securing the tire bead to the rim, and a non-pneumatic tire (donut) within the pneumatic tire to enable a driver to maintain control over the vehicle after a catastrophic pressure loss, and are evolving to the point where it is becoming less and less noticeable to the driver that the tire has become deflated. The broad purpose behind using run-flat tires is to enable a driver of a vehicle to continue driving on a deflated pneumatic tire for a limited distance (e.g., 50 miles, or 80 kilometers) prior to getting the tire repaired, rather than stopping on the side of the road to repair the deflated tire. Hence, it is generally desirable to provide a low-pressure warning system within in the vehicle to alert (e.g., via a light on the dashboard, or a buzzer) the driver to the loss of air in a pneumatic tire. Such warning systems are known, and do not form part of the present invention, per se.
Although the use of pressure transducers in pneumatic tires, in association with electronic circuitry for transmitting pressure data is generally well known, these pressure-data systems for tires have been plagued by difficulties inherent in the tire environment. Such difficulties include effectively and reliably coupling RF signals into and out of the tire, the rugged use the tire and electronic components are subjected to, as well as the possibility of deleterious effects on the tire from incorporation of the pressure transducer and electronics in a tire/wheel system. In the context of xe2x80x9cpassivexe2x80x9d RF transponders which are powered by an external reader/interrogator, another problem is generating predictable and stable voltage levels within the transponder so that the circuitry within the transponder can perform to its design specification.
An example of a pneumatic tire having an integrated circuit (IC) transponder and pressure transducer is disclosed in commonly-owned U.S. Pat. No. 5,218,861, issued Jun. 15, 1993 to Brown, et. al. and incorporated in its entirety by reference herein. This patent describes an RF transponder mounted within a pneumatic tire. Upon interrogation mounted transponder include:
(a) piezoelectric transducers;
(b) piezoresistive devices, such as one of those disclosed in U.S. Pat. No. 3,893,228 issued in 1975 to George, et al., and in U.S. Pat. No. 4,317,216 issued in 1982 to Gragg, Jr.;
(c) silicon capacitive pressure transducers, such as is disclosed in U.S. Pat. No. 4,701,826 issued in 1987 to Mikkor;
(d) devices formed of a variable-conductive laminate of conductance ink; and
(e) devices formed of a variable-conductance elastomeric composition.
It is a broad object of the present invention to provide an improved radio frequency (RF) transponder (xe2x80x9ctagxe2x80x9d) as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
It is a further object of the invention to provide an improved radio frequency (RF) transponder (xe2x80x9ctagxe2x80x9d) capable of transmitting data related to a monitored object and parameters associated with the object to an external reader/interrogator. It is another object of the present invention to provide pressure data from a transponder to an external reader/interrogator in a manner in which temperature-dependency of the pressure data can be eliminated from the pressure data, resulting in a temperature-compensated pressure measurement being displayed by the external reader/interrogator.
According to the invention, a radio-frequency (RF) transponder comprises circuitry capable of transmitting information unique to an object with which the transponder is associated to an external reader/interrogator. Additionally, one or more sensors (transducers) provide real-time parameter measurement at the transducer location. These measurements are transmitted to the external reader/interrogator, in the form of data, in a data stream on a signal which is output by the transponder, such as by impressing (modulating) the data stream onto a RF signal transmitted by the transponder to the external reader/interrogator.
According to an aspect of the invention, the transponder is preferably powered by an RF signal from the external reader/interrogator. However, it is within the scope of this invention that the transponder is battery-powered.
According to an aspect of the invention, the transponder is preferably implemented on a single integrated circuit (IC) chip, with a minimum of external instrumentalities such as an antenna.
According to an aspect of the invention, at least one real-time parameter which is measured is temperature. Preferably, the temperature sensor is embedded (xe2x80x9con-chipxe2x80x9d) in the IC chip of the transponder.
According to an aspect of the invention, an additional real-time parameter which may be measured is pressure. Pressure is preferably measured by a separate (xe2x80x9coff-chipxe2x80x9d) pressure sensor, which is preferably of a type that varies its capacitance value as a function of ambient pressure. Preferably, the temperature sensor is disposed so as to be subject to substantially the same ambient temperature as the pressure sensor so that a true, temperature-compensated pressure can readily be calculated.
According to an aspect of the invention, another additional parameter which may be measured is in the form of an indication that an excessively high temperature condition, albeit transient, has previously occurred. It should be understood that this parameter is different in nature than the real-time parameters of temperature and pressure. An example of a sensor suitable for sensing and indicating that such a transient over-temperature condition has occurred can be found in U.S. Pat. No. 5,712,609, issued Jan. 27, 1998 to Mehregany, et al. and incorporated by reference in its entirety herein. Mehregany""s sensor is cited as being exemplary of a suitable Maximum Temperature Measurement (polling) by an external RF signal provided by a xe2x80x9creaderxe2x80x9d, the transponder transmits tire identification and tire pressure data in digitally-coded form. The transponder is xe2x80x9cpassivexe2x80x9d in that it is not self-powered, but rather obtains its operating power from the externally-provided RF signal. The tire has two spaced beads, each including an annular tensile member of wound or cabled steel wire. The transponder antenna is positioned adjacent one of the annular tensile members for electric or magnetic field coupling to the annular tensile member.
Another example of a pneumatic tire having an integrated circuit (IC) transponder and pressure transducer is disclosed in commonly-owned U.S. Pat. No. 5,181,975, issued Jan. 26, 1993 to Pollack, et. al. and incorporated in its entirety by reference herein. As described in this patent, in a tire that has already been manufactured, the transponder may be attached to an inner surface of the tire by means of a tire patch or other similar material or device.
Another example of an RF transponder in a pneumatic tire is disclosed in commonly-owned U.S. Pat. No. 4,911,217, issued Mar. 27, 1990 to Dunn, et. al. and incorporated in its entirety by reference herein. This patent describes the transponder having two electrodes, a first of which is positioned such that the average spacing of the first electrode""s surface from one of the tire""s steel reinforcing components, such as an annular tensile member in its bead or a steel-reinforced ply, is substantially less than the average spacing of the second electrode""s surface from the reinforcing component. FIG. 1a of this patent also describes a prior art identification system (xe2x80x9creaderxe2x80x9d) that can be used to interrogate and power the transponder within the tire. The identification system includes a portable hand-held module having within it an exciter and associated circuitry for indicating to a user the numerical identification of the tire/transponder in response to an interrogation signal.
Typically, in an IC transponder, the IC chip and other components are mounted and/or connected to a substrate such as a printed circuit board (PCB). For example, a pressure transducer may be mounted to the PCB and wired either directly to the IC chip or indirectly to the IC chip via conductive traces on the PCB. The PCB substrate is suitably a reinforced epoxy laminate having a thickness of twenty mils, and having a glass transition temperature exceeding 175xc2x0 C. (degrees Celsius). A suitable PCB material is available as xe2x80x9chigh performancexe2x80x9d FR-4 epoxy laminate, grade 65M90, sold by Westinghouse Electric Corporation, Copper Laminates Division, 12840 Bradley Avenue, Sylmar, Calif. 91342.
There have thus been described, hereinabove, a number of RF transponders suitable for mounting within a pneumatic tire. The environment within which a tire-mounted transponder must reliably operate, including during manufacture and in use, presents numerous challenges to the successful operation of the transducer. For example, the pressure sensor used with the transponder preferably will have an operating temperature range of up to 125xc2x0 C., and should be able to withstand a manufacturing temperature of approximately 177xc2x0 C. For truck tire applications, the pressure sensor must have an operating pressure range of from about 50 psi (pounds per square inch) to about 120 Psi (from about 345 kp (kilopascals) to about 827 kD), and should be able to withstand pressure during manufacture of the tire of up to about 400 psi (about 2758 kp). The accuracy, including the sum of all contributors to its inaccuracy, should be on the order of plus or minus 3% of full scale. Repeatability and stability of the pressure signal should fall within a specified accuracy range.
The transponder must therefore be able to operate reliably despite a wide range of pressures and temperatures. Additionally, a tire-mounted transponder must be able to withstand significant mechanical shocks such as may be encountered when a vehicle drives over a speed bump or a pothole.
Suitable pressure transducers for use with a tire-Switch (MTMS) for use with the transponder of the present invention. Reference is also made to U.S. Pat. No. 5,706,565 which is incorporated in its entirety by reference herein.
The transponder is primarily intended to be associated with a pneumatic tire, and is preferably located within the tire. However, it is within the scope of this invention that the transponder is associated with another object being monitored, such as an animal.
In a preferred embodiment, the transponder comprises:
circuitry for receiving an RF signal at a first frequency (Fi) from the external reader/interrogator and processing the received RF signal to provide power and clock pulses to other circuitry;
circuitry for controlling window(s) of time during which real-time parameter measurement(s) is (are) made, and captured;
circuitry for storing calibration constants; and
circuitry for impressing (preferably by Phase Shift Keying (PSK) modulation) the captured real-time parameter measurements and excessive temperature condition indication onto a signal which is transmitted back to the external reader/interrogator at a second frequency (Fc) which is different from the first frequency (Fi).
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.